Competitive formation of the methylene and methylene ether bridges in the urea–formaldehyde reaction in alkaline solution: a combined experimental and theoretical study

Отверждение карбамидоформальдегидных смол с различным мольным соотношением в системе карбамид : формальдегид протекает по разным механизмам. Так, при мольном соотношении карбамид : формальдегид 1 : 2 процесс отверждения направлен в сторону образования межмолекулярных связей – метиленовых и метиленэфирных, о чем свидетельствует снижение содержания гидроскиметильных групп. Введение в смолу карбамида до мольного соотношения карбамид : формальдегид 1 : 1,65 приводит к деструкции метиленэфирных связей под действием амидных групп карбамида, формированию на их месте метиленовых мостиков, образованию мономерных продуктов, которые включают в себя карбамид и его гидроксиметильные производные. Curing of urea-formaldehyde resins with different molar ratio in the system urea : formaldehyde flows through different mechanisms. Thus, at a molar ratio of urea : formaldehyde 1 : 2, the curing process is directed towards the formation of intermolecular bonds – methylene and methylene-ether, as evidenced by a decrease in the content of hydroksimethyl groups. The introduction of urea into the resin to the molar ratio urea : formaldehyde 1 : 1.65 leads to the destruction of methylene-ether bonds under the action of amide groups of urea, the formation of methylene bridges in their place, the formation of monomer products, which include urea and its hydroskimethyl derivatives.

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Theoretical Study on the Relative Energies of Anionic Pterin Tautomers

Pteridines ◽

10.1515/pteridines.2009.20.1.124 ◽

2009 ◽

Vol 20 (1) ◽

pp. 124-128 ◽

Cited By ~ 13

Author(s):

Michael Soniat ◽

Christopher B. Martin

Keyword(s):

Aqueous Solution ◽

Density Functional Theory ◽

Aqueous Solutions ◽

Alkaline Solution ◽

Density Functional ◽

Theoretical Study ◽

Density Functional Theory Calculations ◽

Functional Theory ◽

Tautomeric Forms ◽

Chemical And Biological Systems

Abstract Pterins exist as several tautomeric forms and behave as weak acids in aqueous solutions. Therefore, several acidbase equilibria may be present. For several pterin derivatives, the range of the experimental pKa lies in the range 6-8. The anionic form of the lactam structure is the only structure considered in the literature to represent the chemistry of pterins in alkaline solution. In the present study, density functional theory calculations were used to determine the relative energies of various anionic tautomers of pterin present in aqueous solution which may play a role in chemical and biological systems.

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